computer science

High-level design

High-level design is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand High-level design rather than just read about it. In short: High-level design (HLD) explains the architecture that would be used to develop a system. The architecture diagram provides an overview of an entire system, identifying the main components that would be developed for the product and their interfaces.

Key takeaways

High-level design belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect High-level design to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of High-level design from memory before moving on to harder problems.

Reference excerpt

High-level design (HLD) explains the architecture that would be used to develop a system. The architecture diagram provides an overview of an entire system, identifying the main components that would be developed for the product and their interfaces. The HLD can use non-technical to mildly technical terms which should be understandable to the administrators of the system. In contrast, low-level design further exposes the logical detailed design of each of these elements for use by engineers and programmers. HLD documentation should cover the planned implementation of both software and hardware.

Purpose Preliminary design: In the preliminary stages of system development, the need is to size the project and to identify those parts which might be risky or time-consuming. Design overview: As the project proceeds, the need is to provide an overview of how the various sub-systems and components of the system fit together. In both cases, the high-level design should be a complete view of the entire system, breaking it down into smaller parts that are more easily understood. To minimize the maintenance overhead as construction proceeds and the lower-level design is done, it is best that the high-level design is elaborated only to the degree needed to satisfy these needs.

High-level design document A high-level design document or HLDD adds the necessary details to the current project description to represent a suitable model for building. This document includes a high-level architecture diagram depicting the structure of the system, such as the hardware, database architecture, application architecture (layers), application flow (navigation), security architecture and technology architecture.

Design overview A high-level design provides an overview of a system, product, service, or process. Such an overview helps supporting components be compatible with others. The highest-level design should briefly describe all platforms, systems, products, services, and processes that it depends on, and include any important changes that need to be made to them. In addition, there should be brief consideration of all significant commercial, legal, environmental, security, safety, and technical risks, along with any issues and assumptions. The idea is to mention every work area briefly, clearly delegating the ownership of more detailed design activity whilst also encouraging effective collaboration between the various project teams. Today, most high-level designs require contributions from a number of experts, representing many distinct professional disciplines. Finally, every type of end-user should be identified in the high-level design and each contributing design should give due consideration to customer experience.

See also Software development process Systems development life cycle

References

External links High Level Design Document sample format

Worked examples

Example 1 — a first encounter with High-level design

Start with the simplest possible case. Write down what High-level design claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to High-level design before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about High-level design ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of High-level design

In research: High-level design appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses High-level design in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: High-level design is common in secondary-school and first-year university syllabi. It links to neighbouring topics Design, Software design, Software development, so understanding it makes those chapters shorter.
In everyday life: Look for High-level design outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study High-level design in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what High-level design means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain High-level design out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is High-level design in simple terms?

Why does High-level design matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study High-level design?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on High-level design.